Fluorescent material



Patented June 10, 1941 FLUORESCENT MATERIAL Willard A. Roberts, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York No Drawing.

Application March 14, 1940,

Serial No. 323,949 r 3 Claims. (01

My invention relates generally to fluorescent materials and more particularly to novel compositions of fluorescent materials particularly useful in gaseous electric discharge lamps, especially low pressure mercury lamps. Still more particularly, my invention relates to novel compositions of fluorescent materials of the zinc beryllium silicate type. The present application is a continuation-in-part of my application Serial No. 171,953, filed October 30, 1937.

It has been known heretofore that zinc beryllium silicate possessed many desirable properties as a fluorescent material. Such a material, activated with manganese, is disclosed in Patent 2,118,091 to H. W. Leverenz, particularly for use in cathode ray tubes. Patent 2,103,085 to A. H. McKeag et al. discloses the use of such a material in combination with a gaseous electric discharge lamp. In both patents it is stated that the proportions of zinc and beryllium may be widely varied. However, it is also stated that the composition is formed by replacing part of the zinc in zinc orthosilicate (2ZnO.SiOz) by beryllium. In other words the molar sum of the beryllium and zinc is always equal to 2 for each molal of silicon so that the material may be properly termed an orthosilicate of zinc and beryllium.

In accordance with the present invention, 1

have discovered that advantages in eificiency and color'of the light emitted by a fluorescent zinc beryllium silicate are obtained by departing from the proportions found in the orthosilicate. Thus, I have found it desirable to employ a substantially largeramount of silica than is present in the or.-

nese activator than used heretofore.

In the new composition comprising my invention, I prefer to maintain the proportions, by weight, of about 60 parts zinc oxide and 40 parts silica with the beryllium oxide content ranging HESS.

A particularly useful composition emitting a reddish yellow illumination when excited by 2537A. radiation may be prepared by mixing thoroughly 200 grams of silica, 300 grams of zinc oxide (or equivalent amount of zinc nitrate), 26 grams of manganous carbonate (or equivalent amount of manganous nitrate) and 20 grams of beryllium oxide. The mixture may be ground. to pass a 100 mesh silk bolting cloth. It may then be heated at about 1140 C. for one hour and then ground. The heating and grinding may be repeated until the proper color is obtained when the material is excited by a source of 25373. radiation. The material may then be ground to pass a 200 mesh silk bolting cloth. It may then be applied to the interior'surface of the envelope of a discharge lamp by methods now well known in the art, preferably'by suspending the material in a suitable volatilizable binder and flushing the enve- I lope with the suspension, as disclosed, for examparts beryllium oxide to a temperature of about thosilicate and also a higher amount of mangalium oxide as beryllium hydroxide.

1100 C. to 1150 C. for from one to two hours. This material differs from that described, above in that the proportions of both the beryllium and I the manganese have been increased so that the finished material consists of about 60 parts ZnO, 40 parts Siw, 6 parts BeO and 7% parts M1102. The material may be used as a substitute for the 'more expensive cadmium borate in some of the mixtures of. phosphors employed to produce white fluorescent lamps.

If desired, a small amount, say about A part by weight, of lithium chloride may be mixed with the starting materials as a flux. Also, the silica may beintroduced as silicic acid, and the beryl- Also, if desired, the material may be quenched inwater after the final heat treatment, and the firing temperature may be varied somewhat to produce difierent shades of color.

The material comprising my invention is preferably coated on the interior surface of the glass envelope .of a gaseous electric discharge lamp,-

pressure of the order of 12 microns so as to pro- 'duce an abundance of radiations of 25375.. wave-' length.

The reddish yellow, fluorescent material described above is particularly suitable for mixing with other phosphors to produce a white light. For example, it may be mixed with magnesium tungstate to produce a white light, or with magnesium tungstate and cadmium borate to produce a daylight lamp, as described in application Serial No. 236,277, George E. Inman, filed October 21, 1938. The said reddish yellow material may also be coated on the interior of a low pressure mercurydischarge device to produce a gold or yellow lamp in which case a coating of yellowcolored material is preferably also applied to screen out the light other than the yellow light. The said yellow-colored coating is preferably applied to the inner surface of the envelope before the coating of fluorescent material is applied thereto.

What I claim as new and desire to secure by Letters Patent 01 the United States is:

1. A fluorescent zinc beryllium silicate for gaseous electric discharge lamps containing a source of ultraviolet radiation comprising by weight approximately 60 parts zinc oxide, parts silica, 1 to 10 parts beryllium oxide and 2 to 10 parts manganese dioxide.

2. A fluorescent zinc beryllium silicate for gaseous electric discharge lamps containing a source of ultraviolet radiation comprising by weight approximately parts zinc oxide, 40 parts silica, 4 parts beryllium oxide and 4 parts manganese dioxide.

3. A fluorescent zinc beryllium silicate for gaseous electric discharge lamps containing a source of ultraviolet radiation comprising by weight approximately 60 parts zinc oxide, 40 parts silica, 6 parts beryllium oxide and 7%. parts manganese dioxide.

WILLARD-A. ROBERTS. 

